The present invention relates to a method for making earthen blocks, particularly cold stabilized blocks, comprising the following steps:
filling a mold cavity with a material to be molded, the material comprising at least earth;
applying a first compression force on said material by moving a punch;
driving the walls of the mold cavity by the material to be molded into the same direction as the first compression force while maintaining the first compression force.
The invention relates also to a device for making earthen blocks, particularly cold stabilized blocks, comprising a hopper, a filling unit for filling said hopper with a material to be molded and a means for moving said hopper, for bringing the hopper towards a mold cavity and for emptying the material into said mold cavity. The device further includes a press for compressing said material introduced into the mold cavity and for forming a block of the material. The press includes a first press having a first punch, and also a first means for moving the walls of the mold cavity in the same direction as the first punch.
Such a method and such a device are known from the Belgian Patent No. 877,553. In the known device a hopper is filled with a material to be moulded, particularly a previously mixed material formed by earth or sand, cement and water. The hopper is moved above a mould cavity wherein it is emptied. Then a press with a punch applies pressure to the material introduced into the mold cavity to compress this material and to make a block or a brick of the latter. During the mold operation by compression, the walls of the mold cavity are moved by the driving effect of the mass to be molded, the density of which increases.
A drawback of the method and the device is the driving effect of the mass to be moulded is small and consequently the compression of the material is not realized in an adequate manner. This causes a malformation of the blocks such that the blocks are unusable.
An object of the invention is to realize a method and a device which solves this drawback.
To this end a method according to the invention is characterized in that after the filling step and before applying said first force, a precompression force smaller than the first force is applied to the material to be molded by means of said punch.
A device according to the invention is characterized in that the press comprises second means for applying a precompression force by the first punch smaller than the compression force to the material to be molded.
The precompression allows the material introduced into the mold cavity to set and to eliminate hollows which would have been formed during the filling. When the material has been set by means of the precompression, the energy applied during the compression is better distributed over the whole material and the driving effect of the mass to be molded against the walls of the mold cavity provides a better compression and a more efficient formation of the blocks.
It has to be noted that the application of different compression forces during the manufacture of one single block is described in the French Patent No. 325,964. A method of manufacturing blocks is described wherein a first compression is followed by a big compression is applied. However, the big compression is not applied uniformly onto the two opposed sides of a block and the walls of the mold cavity are driven in an hazardous way which does not allow a uniform compression and adequate control of the compression method. The method according to the present invention is distinguished from the French Patent No. 325,964 because the walls of the mold cavity in the present invention remain motionless during the precompression and are only driven when applying the first compression force. In said French Patent, the walls move during the initial compression and remain motionless during the big compression. The fact that the walls move during the first compression leads to a malformation of the blocks.
A preferred embodiment of a method according to the invention is characterized in that at about the end of said emptying of the hopper, an impulse of compressed air is injected into said hopper. The impulse of compressed air allows a better emptying and a better filling which results in better block formation.
Often the hopper is not filled appropriately because hollows are formed. As a result the hopper is filled insufficiently and an unusable block is created since the block is to fragile due to a lack of homogeneity. In order to remedy this problem a device according to the invention, a verification unit verifies by means of an ultrasonic signal if the hopper has been filled up to a predetermined level. The verification unit omits a control signal in case of an insufficient filling. The verification unit makes it relatively. Moreover, the use of an ultrasonic signal allows control of the filling of the hopper without a measuring element in the hopper. The control signal generated insufficient filling prevents an heterogeneous block.
A preferred embodiment of a device according to the invention is characterized in that the verification unit is connected to the filling unit generates under control of said control signal, a filling signal to the filling unit to activate the latter. This allows further filling when an insufficient amount of material has been introduced into the hopper.
Preferably the verification unit measures the filling level of said hopper and incorporates into said filling signal an indication of how much additional materials is to be added to reach said predetermined level. In this way the amount of material to be added can be determined.
Another preferred embodiment of a device according to the invention is characterized in that said hopper is connected to a vibration unit for vibrating said hopper. In this way, the formation of hollows is avoided.
Preferably the vibration unit includes a needle which vibrates at an ultrasonic frequency. The ultrasonic vibrations eliminate the hollows.
Preferably the blocks made by applying the method according to the invention are nesting blocks having a predetermined height with a tolerance of less than 2%. This allows a construction without jointings and without rough-casting.
The invention will now be described more into detail with reference to the drawings which represent an embodiment of a device according to the invention. It will be clear that the invention is not limited to the illustrated example and that other embodiments are also possible within the scope of the invention.